Reflector device for emitting a plurality of reflected beams from a single main light beam

The present invention relates to the field of optical and/or optronic systems. More particularly, the invention relates to the field of imaging, for example of scenes, or to the detection field.

More particularly, the invention relates to a reflector device provided with a plurality of mirrors arranged so as to form a plurality of reflected beams from one and the same incident light beam. The mirrors are advantageously movable on one or more pivot axes so that each beam reflected by a given mirror sweeps a surface as soon as a movement is imposed on said mirror.

Micro-mirrors are now widely present in the MEMS field and in particular in devices of the LIDAR type (“Light Detection and Ranging systems”).

These make it possible in particular to sweep a surface or a target with light radiation for detection or imaging purposes.

In this regard, in these devices of the LIDAR type, the micro-mirrors are arranged to oscillate on one or two pivot axes, at a predetermined sweep frequency, so as to reflect an incident radiation in various directions.

The sweep frequency of the micro-mirrors can vary from a few Hz to several kHz, and their size can be of the order of a few tens of micrometres to several millimetres (for example a few millimetres in diameter for micro-mirrors in disc form), and can in particular be between 500 μm and 10 mm.

(extracted from document [1] cited at the end of the description) illustrates a first possible architecture of a device provided with two micro-mirrors, referred to respectively as first micro-mirrorand second micro-mirror, arranged to pivot about, respectively, a first pivot axis XX′ and a second pivot axis YY′ that are non-parallel. In particular, these two micro-mirrorsandare arranged so that a light beam emitted by a light sourceis reflected by the first micromirrorin the direction of the second micromirror, which reflects it in its turn in the direction, for example, of a screen. The rotation of each of the micro-mirrorsandabout their respective pivot axes thus makes it possible to sweep a surface with the light beam, for example for imaging or detection purposes.

Such an architecture is however not satisfactory.

This is because this architecture requires precise alignment of the two micro-mirrors and is consequently difficult to implement.

Moreover, the area able to be swept by the light beam remains relatively limited.

A second architecture, illustrated in(extracted from document [1] cited at the end of the description), can be envisaged. This uses a single micromirrormounted so as to pivot about two pivot axes XX′ and YY′ that are non-parallel. The oscillation of this micromirrorabout each of the two pivot axes XX′ and YY′ thus makes it possible to sweep the surface of a screenby means of a light beam coming from a light sourceand reflected by said micromirror.

However, this second architecture is also not satisfactory.

This is because the latter, although simpler to integrate, does not make it possible to sweep large surfaces with the light beam.

One of the aims of the present invention is therefore to propose a reflector device that offers greater flexibility in terms of sweep area.

In particular, one aim of the present invention is to propose a reflector device able to sweep a surface with a greater extent than the known devices of the prior art.

Another aim of the present invention is to propose a device, certain electro-optical or optical performances of which, such as angular resolution, are improved compared with the known devices of the prior art.

The aims of the present invention are, at least partly, achieved by a reflector device intended to form N reflected beams from a principal light beam, the device comprises:

According to one embodiment, each mirror is mounted so as to pivot about one or more pivot axes, and is associated with one or more actuators arranged to pivot said mirror on one or other or both of the pivot axes, advantageously an actuator comprises at least one of the elements selected from: an electrostatic actuator, a magnetic actuator, a piezoelectric actuator, a thermal actuator. For example, mirrors having two pivot axes can be provided.

According to one embodiment, the N mirrors are arranged on successive parallel planes so that the centres of the N mirrors are essentially aligned on the principal axis.

According to one embodiment, the N mirrors each have a circular shape, and a radius increasing from the first position to the Nposition in the principal order.

According to one embodiment, N is equal to 2, and the reflector device also comprises a secondary mirror arranged so that a secondary beam incident on the front face of the mirror in first position is firstly partially reflected by said front face and secondly partially transmitted by the rear face of said mirror and then reflected by a secondary front face of the secondary mirror.

According to one embodiment, said reflector device comprises a secondary light source able to emit the secondary light beam.

According to one embodiment, the secondary mirror is arranged so that the respective centres of the secondary mirror and of the mirror in first position define an axis, referred to as secondary axis, different from the principal axis, and wherein the secondary light source is arranged so that the secondary light beam is emitted on the secondary axis.

According to one embodiment, optical elements are used to convey the light beam transmitted by the rear face of a mirror in a given position to the front face of the mirror in the following position in the principal order.

According to one embodiment, an optical element comprises at least one of the components selected from: a prism, a deflector mirror, a lens.

According to one embodiment, each mirror comprises, from its front face to its rear face, a partially reflective layer and a mechanical support layer.

According to one embodiment, the partially reflective layer comprises a Bragg stack, the Bragg stack comprising at least one elementary Bragg stack.

According to one embodiment, an elementary Bragg stack comprises a stack of two dielectric and/or semiconductor layers. Advantageously, the elementary Bragg stack comprises a layer of amorphous silicon and a layer of silicon oxide.

According to one embodiment, the Bragg stack is limited to one or two elementary Bragg stacks.

According to one embodiment, the mechanical support layer comprises a semiconductor material, advantageously silicon, even more advantageously monocrystalline silicon.

According to one embodiment, the N mirrors are arranged so that each of the N light beams sweeps a different surface.

According to one embodiment, at least one mirror is arranged so that the surface swept by the light beam reflected by the front face of the mirror in question has a reduced extent compared with the surfaces swept by the other reflected light beams.

According to one embodiment, at least one mirror among the N mirrors forms an optical filter or spectral filter (wavelength filter).

Advantageously, the light beam has a wavelength of between 1400 nm and 1700 nm, preferably 1550 nm.

According to one embodiment, among said N mirrors, the one arranged in first position is configured to transmit, to a mirror arranged in second position, the principal light beam incident at more than 50%.

The present invention relates to a reflector device intended to form a plurality of independent light beams from a single or from one and the same light source. The reflector device, according to the present invention, comprises, in this regard, a plurality of mirrors configured to partially reflect and transmit an incident beam on their front face. The mirrors are thus arranged, in an order, from a first position to an Nposition, so that a principal light beam incident on the front face of the mirror in first position interacts successively, and in the order, with each mirror to form a beam reflected by the front face and a beam transmitted by the rear face of the mirror in question. More particularly, the beam reflected by the front face of the mirror in a position i, i between 2 and N, results from the reflection of the beam transmitted by the rear face of the mirror in position i−1.

is a schematic representation of a reflector deviceaccording to a first embodiment of the present invention.

This reflector devicecomprises in particular N (N integer greater than or equal to 2) mirrors (with for example N=3 mirrors,,shown on) assembled on a support. Assembling each of the mirrorstomay involve an intermediate supporttoresting on the support.

The reflector devicealso comprises a light sourcearranged to emit a principal light beam on a principal axis AA′. The principal light beam may be a polychromatic radiation, and in particular may cover a continuous range of wavelengths, for example in the infrared domain (between 900 nm and 2100 nm). Alternatively, the principal light beam may be quasi-monochromatic or even monochromatic, in particular a laser, with a wavelength preferably between 1400 nm and 1700 nm, preferentially 1550 nm.

Each mirror(with i between 1 and N) is in particular configured to partially reflect, through a front face, the light beam, able to be emitted by the light source, incident on said front face, and to partially transmit said light beam through a rear faceopposite to the front face. In other words, each mirroris partially reflective through its front face, and partially transparent with regard to the light beam able to be emitted by the light source.

According to the present invention, the mirrorstoare arranged, in an order, from a first position to an Nposition, so that the principal light beam, incident on the principal front faceof the mirrorin first position, successively passes through, in the order, all the mirrorsto.

More particular, according to this first embodiment, the N mirrorstoare arranged on successive parallel planes Pto P(only the planes P, Pand Pare shown on) and so that the centres of the N mirrors are essentially aligned on the principal axis.

Thus the principal light beam finteracts successively, in the order, with the mirrorsto. The principal beam interacts firstly with the first mirror, and produces a reflected beam fand a transmitted beam f. This phenomenon is reproduced at the second mirror. More generally, as illustrated in, the interaction of the principal light beam fwith a given mirrorresults in particular in the formation of a beam freflected by its front faceand a beam ftransmitted by its rear face. More particularly, the beam freflected by the front faceof a mirror in a position i, i between 2 and N, results from the reflection, on said front face, of the beam ftransmitted by the rear faceof the mirror in position i−1.

Thus the reflector deviceaccording to the present invention makes it possible to form N independent reflected beams with a single or one and the same principal light beam f.

Still in relation to, the mirror, in first position, can be adapted to fully reflect (f) a first range of wavelengths of the principal range, and to transmit (f) the other wavelengths. The mirror(in second position), for its part, can be adapted to reflect (f) a second range of wavelengths different from the first range.

According to a particular embodiment, the first mirror, disposed in first position, can be adapted to transmit an incident light beam, in particular an incident laser beam, at more than 50%.

In this case, preferably the more superimposed micro-mirrors the device includes, the greater the transmission by the first mirror is designed to be. The percentage of transmission between each mirror is then adapted according to the number of mirrors and the applications sought.

Particularly advantageously, each mirrortois mounted so as to pivot about one or more pivot axes, for example two pivot axes, and is associated with one or more actuatorstoarranged to pivot said mirror on one and/or other of the pivot axis. Still advantageously, an actuatortocan comprise at least one of the elements selected from: an electrostatic actuator, a magnetic actuator, a piezoelectric actuator, a thermal actuator.

The actuators may, moreover, be controlled by control means, for example provided with at least one microprocessor.

The rotation of a mirrorabout its pivot axes,, advantageously perpendicular, thus makes it possible to sweep a surface with the beam freflected by the front face, for example for imaging or detection purposes. In the example illustrated on, two pivot axes,are formed by arms,,,. In the example illustrated on, a mirroris provided with a single pivot axisformed for example by two arms,. A different number of sweep axes and support arms, in particular greater, can be provided.